Biodegradation of selected xenobiotic compounds: Chlorinated phenols and 2,4,6-trinitrotoluene.

摘要

Microbial degradation of substituted aromatic compounds was studied under aerobic conditions. Target compounds included, phenol, 2,4-dichlorophenol, pentachlorophenol, and 2,4,6-trinitrotoluene. These compounds tend to inhibit dioxygenase attack of the benzene ring due to the presence of electron-withdrawing characteristics of substituted nitro- or chloro-groups.; Biodegradation of phenolic compounds under multiple substrate conditions revealed significant substrate interactions affecting the growth of the microorganisms. The presence of the growth substrate, phenol, increased the growth of a mixed culture on other chlorinated phenols. After the introduction of chlorinated phenols, a decrease in microbial species diversity was observed resulting in a change of the kinetic constants. The remaining culture had higher substrate affinity, lower growth rate, and was more susceptible to inhibitory effects of chlorinated phenols.; Under carbon and nitrogen limited conditions in fed-batch reactors, the biotransformation of TNT was investigated. Results showed that the rate of intermediates formation depended on the substrate condition. Nine aerobic bacterial species were isolated from a soil contaminated with munitions waste from a site in Illinois. These species were tentatively identified as: one Enterobacter sp., one Pseudomonas sp., and seven Alcaligenes spp.; With two of the best performers out of the nine isolates, the effects of culture conditions on TNT transformation were studied. TNT was transformed faster in the presence of high concentrations of supplemental carbon sources and azoxy-compound formation was minimized by decreasing culture pH. The presence of nitrogen sources in any form did not affect TNT transformation by Alcaligenes sp. I15. However, the presence of a nitrogen source as nitrate significantly inhibited TNT transformation by Enterobacter sp. I5.; Enterobacter sp. I5 mineralized TNT (3.2%) after 10 days of incubation in the respirometer and the result was reproducible. Unknown polar intermediates were identified by GC-MS analysis. New intermediates identified were 4-acetamido-2,6-nitrotoluene, 4-acetamido-2-amino-6-nitrotoluene, 4-amino-2-nitrotoluene, 4-acetamido-2-nitrotoluene, and 3-methylcatechol. Results showed that transformation of TNT by Enterobacter sp. I5 involves a combination of acetylation, reduction, and deamination. Aerobic mineralization of TNT was possible, however, it might be necessary to increase the amount of mineralization by further optimizing culture conditions.